[SPIRV][Question]Link libraries

[Vincent-P]

Hi,
I saw that SPIRV have a Linkage capability and can import and export functions or global variables.
SPIRV-Tools also has an experimental linker to combine spirv files.

So is it possible to compile a module with the lib_6_3 target profile that exports some functions, and import those in a separate file?

[jaebaek]

@Vincent-P Thank you for opening this issue. As far as I know, we do not generate relocatable code, but I am not 100% sure. I will get back to you after researching on it.

[jaebaek]

Hi @Vincent-P , unfortunately, we currently do not support a compilation of a relocatable code. lib_6_3 and lib_6_4 are used only for the ray tracing code but used for general code.
For the relocatable code generation, we may need some big changes in the source code.

In addition, as far as I know, spirv-link is also work-in-progress. See here.

[Vincent-P]

Okay, thanks for your answer!

[gongminmin]

Any plan to support lib_6_x profile?

[ehsannas]

@gongminmin I'm wondering what specifically you are referring to? Is there a document/reference that you can point us to?

If you're referring to using [shader(...)] for raytracing purposes, it is supported (example).

If you're referring to a more broad scope, can you please provide an example and/or the lib_6_* doc/spec?

[gongminmin]

Currently HLSLs can be compiled to Dxil modules as general purpose lib_6_x, and linked to pixel shader, vertex shader, etc. (https://github.com/microsoft/DirectXShaderCompiler/blob/master/tools/clang/unittests/HLSL/LinkerTest.cpp). Can SPIR-V back-end do the same thing? Thanks.

[ehsannas]

IIUC the linking stage is also done offline (via DXC), not at runtime. right?

[ehsannas]

Thanks for the reference. The SPIR-V spec has the Linkage capability.
At a high level, to get that to work we'd need do a few things:

1. the SPIR-V backend in DXC to generate proper linkage information.
2. spirv-link inside SPIRV-Tools currently only works for OpenCL, so there's some work that needs to be done there in order to properly link binaries and generate a SPIR-V that's valid for Vulkan.
3. Since SPIRV-Tools is already included as a dependency, we should be able to use it to link multiple spir-v binaries and generate one valid SPIR-V binary.

[ehsannas]

This is something that we should probably invest time in since we want to create a similar experience for the HLSL developers targeting Dxil and SPIR-V.

[side: I haven't dived into the Vulkan spec to check the finer details. There might be something in there that makes this effort more difficult/impossible ...]